The referenced patent application discloses a leak detection system that employs a differential flow sensing principle for detecting fuel vapor leakage from the evaporative emission system of an automotive vehicle during a leakage test that involves closing the canister purge solenoid (CPS) valve and then positively pressurizing that portion of the evaporative emission system that is upstream of the CPS valve relative to the engine. One of the significant advantages of that leak detection system is that it less complicated, and hence more economical and reliable, than prior systems not using the differential flow sensing principle.
While the present invention also utilizes a differential flow sensing principle, it does so in a new and unique way that is less influenced by certain variables, such as ambient temperature, pressure, engine manifold vacuum, or supply voltage. Accordingly, a leak detection system embodying principles of the present invention possesses potential for improved accuracy and for avoiding false readings that might otherwise arise on account of such variables. More specifically, the inventive leak detection system is capable of canceling out effects of three external variables by comparing the leakage flow with a known calibrated reference leakage. The inventive leak detection system also eliminates the need for a relatively expensive pressure transducer used in prior non-differential flow sensing systems to detect pressure decay. It also does not require a canister vent valve used in such prior systems.
Another aspect of the invention relates to the physical integration of certain components of the leak detection system with a fuel vapor collection canister. This aspect provides greater spatial economy (i.e. more compactness) so that when the integrated canister/system is installed in an automotive vehicle, a smaller amount of space is taken up. This savings in space is especially important to many automobile manufacturers, who must build vehicles that comply with both applicable evaporative emission laws and regulations and applicable fuel economy laws and regulations. The integration possesses the further advantage of requiring fewer connections of components in the automotive assembly plant, and this affords the opportunity for installation cost savings while at the same time an opportunity for increased reliability of the installation.
Still another advantage of the invention is that a fuel vapor leak detection test can be performed either when the engine is running or not running.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.